That's unfortunate, all you can do is go back in 3 months and get tested. The fact that it was in water may have no bearing, unless it was rinsed out completely before being placed in the water bottle. If it was rinsed out completely you likely lucked out and wont be infected. good luck!!
In a situation where a health care worker has experienced an accidental needle stick involving a patient with known hep c the odds of transmission are about 1.8% so in the situation you have described your odds would be proportionately that much lower.
However even if with the very low odds of getting hep c from this incident there are treatments now available that can cure hep c for the majority of patients. So even if you did ever contract hep c you can be cured with these new meds available now.
Also hep c is a very slowly acting illness taking for most people decades to cause liver damage so hep c is not a medical emergency even waiting a year or 2 would likely have no impact on your health.
I whould not waste any energy dwelling on this event just get tested when your doctor recommends to and move on with your life. Worry never robs today of its sorrows it only saps today of its strength.
Which brings me to a question if your son has hep c has he looked into getting treatment to cure him?